Vehicle seats in certain types of vehicles, such as military vehicles, must be designed so that a person sitting in the seat is retained in the seat if the vehicle is exposed to strong jolts due to uneven ground surface or if the vehicle overturns. In addition, the vehicle may be exposed to very strong jolts by an explosive charge, such as a mine, that detonates under the vehicle. When an explosive charge detonates under the vehicle, the person sitting in the seat is exposed for a very large upward directed force, resulting in that the person may hit the vehicles ceiling and become injured. The vehicle can be an off-road vehicle, such as an articulated tracked vehicle which has a front and rear vehicle portion which is controllably interconnected with a controller.
The document US-A1-2010/0219667 discloses a vehicle seat with a pretensioner, which is activated by a downward movement of the seat in the event of an explosion or a strongly downward motion of the vehicle, such as a hard landing of a helicopter. Thus, the entire seat moves down to activate the pretensioner. The pretensioner actuates a shoulder belt, pushing the person down and back in the seat when the belt is stretched. Thereby resulting in a compression of the person's spine.
In certain types of vehicles it is desirable to mount several seats in a limited space, which results in that each seat must be compact and have a low weight. It is also important that the seat does not get in the way inside the vehicle because personnel will go in and out of the vehicle. It is also desirable that the design of the seat is simple and that the construction is reliable, since the seat has a safety function in the vehicle seat.